The principal objectives of this proposal will be to purify and characterize enzymes (arylesterases) implicated in the detoxification of bacterial endotoxins. The sources of these enzymes will be human serum and rabbit peritoneal macrophages. Purification of the detoxifying enzymes and the isolation of major endproducts will be achieved by various column chromatographic techniques. Preparative isoelectric focussing will be done to prepare reasonable quantities of the enzymes from serum and macrophages. It is intended also to isolate and characterize endproducts of detoxification which are produced in vivo.